One good way to develop in PL/pgSQL is to use the text editor of your
choice to create your functions, and in another window, use
psql to load and test those
functions. If you are doing it this way, it is a good idea to
write the function using CREATE OR REPLACE
FUNCTION. That way you can just reload the file to update
the function definition. For example:

While running psql, you can
load or reload such a function definition file with:

\i filename.sql

and then immediately issue SQL commands to test the
function.

Another good way to develop in PL/pgSQL is with a GUI database access tool
that facilitates development in a procedural language. One
example of such a tool is pgAdmin, although others exist. These tools
often provide convenient features such as escaping single quotes
and making it easier to recreate and debug functions.

The code of a PL/pgSQL
function is specified in CREATE
FUNCTION as a string literal. If you write the string
literal in the ordinary way with surrounding single quotes,
then any single quotes inside the function body must be
doubled; likewise any backslashes must be doubled (assuming
escape string syntax is used). Doubling quotes is at best
tedious, and in more complicated cases the code can become
downright incomprehensible, because you can easily find
yourself needing half a dozen or more adjacent quote marks.
It's recommended that you instead write the function body as a
"dollar-quoted" string literal (see
Section
4.1.2.4). In the dollar-quoting approach, you never double
any quote marks, but instead take care to choose a different
dollar-quoting delimiter for each level of nesting you need.
For example, you might write the CREATE
FUNCTION command as:

Within this, you might use quote marks for simple literal
strings in SQL commands and $$ to
delimit fragments of SQL commands that you are assembling as
strings. If you need to quote text that includes $$, you could use $Q$,
and so on.

The following chart shows what you have to do when writing
quote marks without dollar quoting. It might be useful when
translating pre-dollar quoting code into something more
comprehensible.

1 quotation mark

To begin and end the function body, for example:

CREATE FUNCTION foo() RETURNS integer AS '
....
' LANGUAGE plpgsql;

Anywhere within a single-quoted function body, quote
marks must
appear in pairs.

2 quotation marks

For string literals inside the function body, for
example:

a_output := ''Blah'';
SELECT * FROM users WHERE f_name=''foobar'';

In the dollar-quoting approach, you'd just write:

a_output := 'Blah';
SELECT * FROM users WHERE f_name='foobar';

which is exactly what the PL/pgSQL parser would see in either
case.

4 quotation marks

When you need a single quotation mark in a string
constant inside the function body, for example:

a_output := a_output || '' AND name LIKE ''''foobar'''' AND xyz''

The value actually appended to a_output would be: AND
name LIKE 'foobar' AND xyz.

In the dollar-quoting approach, you'd write:

a_output := a_output || $$ AND name LIKE 'foobar' AND xyz$$

being careful that any dollar-quote delimiters around
this are not just $$.

6 quotation marks

When a single quotation mark in a string inside the
function body is adjacent to the end of that string
constant, for example:

a_output := a_output || '' AND name LIKE ''''foobar''''''

The value appended to a_output would then be: AND name LIKE 'foobar'.

In the dollar-quoting approach, this becomes:

a_output := a_output || $$ AND name LIKE 'foobar'$$

10 quotation marks

When you want two single quotation marks in a string
constant (which accounts for 8 quotation marks) and this
is adjacent to the end of that string constant (2 more).
You will probably only need that if you are writing a
function that generates other functions, as in Example
40-9. For example:

To aid the user in finding instances of simple but common
problems before they cause harm, PL/PgSQL provides additional checks. When enabled, depending on the
configuration, they can be used to emit either a WARNING or an ERROR
during the compilation of a function. A function which has
received a WARNING can be executed
without producing further messages, so you are advised to test
in a separate development environment.

These additional checks are enabled through the
configuration variables plpgsql.extra_warnings for warnings and
plpgsql.extra_errors for errors. Both
can be set either to a comma-separated list of checks,
"none" or "all". The default is "none". Currently the list of available checks
includes only one:

shadowed_variables

Checks if a declaration shadows a previously defined
variable.

The following example shows the effect of plpgsql.extra_warnings set to shadowed_variables: